1. Field of the Invention
The present invention relates to a method of forming a thin film transistor (TFT) and a reflective electrode having recesses or projections in a predetermined area and also to a liquid crystal display device to which the method is applied.
2. Description of Related Art
In recent years, a liquid crystal display device provided with TFTs has been widespread rapidly. When the liquid crystal display device is constructed as a reflective type or a transflective type, not only a TFT but also a reflective electrode for reflecting an outer light are provided in each pixel area. In the liquid crystal display device provided with the reflective electrode, the reflective electrode is often provided with recesses or projections in order to improve a quality of the image to be displayed.
For example, In the case where the TFT provided in each pixel area has the top gate structure, the gate electrode is formed by performing a lithographic step before forming the reflective electrode. Next, a photosensitive film is formed and is patterned into a shape having a number of recesses or projections and then a reflective electrode is formed thereon. A lithographic step comprises a plurality of steps including an exposure step, a development step and others. Therefore, in the case where, after forming the gate electrode by performing the lithographic step, the photosensitive film is formed and then patterned into the shape with a number of recesses or projections, there arises a problem that the number of manufacturing steps and the manufacturing costs increase.
It is therefore an object of the present invention is to provide a method of forming a TFT and a reflective electrode comprising recesses or projections with a reduced number of manufacturing steps and reduced costs and a liquid crystal display device to which such method is applied.
A method of the present invention for achieving the object described above is a method of forming a TFT and a reflective electrode having recesses or projections in a predetermined area, the method forming at least a gate electrode and a gate bus by processing a first film, the method comprising the step of forming the first film, the step of forming a photosensitive film on the first film, the step of patterning the photosensitive film in such a way that a first portion, a second portion and a third portion of the photosensitive film remain, the first portion corresponding to the gate electrode, the second portion corresponding to the gate bus and the third portion being different from the first and second portions, the step of etching the first film by using the first, second and third portions as masks and the step of forming the reflective electrode in such a way that at least a portion of the reflective electrode is present on at least the third portion of the first, second and third portions.
According to the present invention, in the step of patterning a photosensitive film, the photosensitive film is patterned in such a way that the first, second and third portions of the photosensitive film remain (the first portion corresponds to the gate electrode, the second portion corresponds to the gate bus and the third portion is different from the first and second portions). Further, in the etching step, the first film is etched using the first, second and third portions of the photosensitive film as etching masks, so that gate electrodes and gate buses can be formed from the first film. After that, in the step of forming a reflective electrode, the reflective electrode is formed without removing the first, second and third portions. Therefore, the shape of the reflective electrode can be adjusted depending on the shape of the first, second and third portions, so that it is possible to provide the reflective electrode with recesses or projections.
As described above, in the present invention, the photosensitive film is used as etching masks for forming the gate electrode and the gate bus and is also used to provide the reflective electrode with the recesses or projections. That is to say, a member used as etching masks for forming the gate electrode and the gate bus and another member for providing the reflective electrode with the recesses or projections are formed from the same photosensitive film. Therefore, there is no need to form, from different photosensitive films, a member used as etching mask for forming the gate electrode and the gate bus and another member for providing the reflective electrode with the recesses or projections, so that the number of manufacturing steps and the manufacturing costs will be reduced.
In the present invention, the third portion may comprise a plurality of parts scattered in the predetermined area or comprise a plurality of holes in the predetermined area.
By constructing the third portion described above, the reflective electrode can be provided with recesses or projections
Further, in the present invention, an edge of the second portion may comprise a curved form.
By providing the edge of the second portion with the curved form, the reflective characteristics of the reflective electrode can be further improved.
A liquid crystal display device of the present invention is a liquid crystal display device comprising a substrate on which a TFT and a reflective electrode having recesses or projections are formed in a predetermined area, wherein the reflective electrode is formed by using the method as claimed in any one of claims 1 to 4.
Further, in the liquid crystal display device of the present invention, the third portion can be present below the reflective electrode and a material of the first film can be present below the third portion.
Furthermore, in the liquid crystal display device of the present invention, an edge of at least that portion of the gate bus, which is located below the reflective electrode, may comprise a curved form.
The invention further relates to a substrate on which a TFT and a reflective electrode having recesses or projections are formed in a predetermined area, the substrate further comprising:
a first film patterned to comprise a first portion, a second portion and a third portion, the first portion forming a gate electrode of the TFT, the second portion forming a gate bus, the third portion being different from the first and the second portion, and at least the third portion being formed in the predetermined area;
provided on the substrate provided with the first film, a photosensitive film patterned to comprise a first photosensitive portion, a second photosensitive portion and a third photosensitive portion, the first portion being masked by and aligned with the first photosensitive portion, the second portion being masked by and aligned with the second photosensitive portion, and the third portion being masked by and aligned with the third photosensitive portion;
provided on the substrate provided with the photosensitive film, a reflective electrode covering at least the third photosensitive portion of said first, second and third photosensitive portions and an area of the substrate adjacent the third photosensitive portion to form the reflective electrode having recesses or projections in a predetermined area and a liquid crystal display device comprising such.